A highly potent derivative of
doxorubicin,
2-pyrrolinodoxorubicin (AN-201), was linked to [D-Lys6]
luteinizing hormone-releasing hormone (
LH-RH) to form a cytotoxic analogue,
AN-207, that can be targeted to
LH-RH receptors. The effects of
AN-207 were investigated in MDA-MB-435 human
estrogen-independent
breast carcinomas, which express
LH-RH receptors. In experiment 1, nude mice bearing orthotopically implanted
tumors received a single i.v. injection of
AN-207,
AN-201, or the carrier at 250 nmol/kg. Five weeks after administration of
AN-207,
tumor volume was significantly decreased by 66% (P < 0.001) and
tumor burden by 71% (P < 0.05) as compared with controls, but no significant effects occurred in other groups. Six of eight (75%) control animals and 37.5% of mice treated with
AN-201 developed
metastases in the lymph nodes, whereas no lymphatic spread was found in any of the mice that received
injections of
AN-207. The antitumor effect of
AN-207 could be partially blocked by pretreatment of the
tumor-bearing mice with high doses of agonist [D-Trp6]
LH-RH, which suggests that
AN-207 acts on
LH-RH receptors on
tumors. The mortality due to toxicity was 25% in the group receiving
AN-201 and 12.5% in the AN-207-treated group. Radioligand binding assays revealed the presence of high-affinity binding sites for
LH-RH on
tumor membranes, and
mRNA for
LH-RH receptors was demonstrated by reverse transcription-PCR. In experiment 2, two i.v.
injections of
AN-207 or
AN-201 at 150 nmol/kg were given on days 0 and 28 to mice bearing orthotopic xenografts of MDA-MB-435. The outcome of the treatment was similar to that observed in experiment 1, but without any toxicity-related deaths.
Tumor growth inhibition and prevention of metastatic disease suggest that cytotoxic
LH-RH analogue
AN-207 could be considered for the treatment of human
estrogen-independent breast
cancers expressing receptors for
LH-RH.